This application is based on Japanese Patent Applications No. 2001-341620 filed on Nov. 7, 2001 and No. 2001-353508 filed on Nov. 19, 2001 the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a fuel injection system that has a safety valve for keeping fuel pressure below a predetermined pressure, specifically, the present invention provides a method of and apparatus for executing a failsafe control when the safety valve is activated.
2. Description of Related Art
Generally, a conventional fuel injection system pressurizes fuel and supplies pressurized fuel to cylinder through an injector. In order to keep a fuel pressure within an appropriate range, the fuel injection system may have a safety valve for discharging pressurized fuel from an accumulator or the like when the fuel pressure exceeds a predetermined pressure. The safety valve may be called as a pressure suppresser, a relief valve or a pressure limiter. The safety valve enters an opened state in response to a fuel pressure exceeding the limit setting pressure.
A common rail type fuel injection system is known as a fuel injection system for diesel engines. The common rail type fuel injection system handles high-pressure fuel. Therefore, it is required not only to keep fuel pressure within a predetermined appropriate range, but also to keep the engine running even if the safety valve is activated.
A high-pressure supply pump accumulates high-pressure fuel in a common rail serving as an accumulator by applying a pressure to the fuel in an operation called a pressure feed operation. The high-pressure fuel accumulated in the common rail is then distributed to a plurality of injectors each provided on a cylinder employed in a multi-cylinder engine. The high-pressure fuel distributed to the injectors is finally injected and supplied into a combustion chamber. An inlet metering valve provided at the inlet of the high-pressure supply pump. The inlet metering valve is used for changing and adjusting fuel volume discharged by the high-pressure pump to the common rail by adjusting the intake volume of fuel introduced into the inlet of the high-pressure supply pump. The high-pressure pump is driven by the engine.
A pressure limiter is provided on at least one of a fuel pipe connecting the high-pressure supply pump to the injectors and the common rail. The pressure limiter discharges fuel from the fuel pipe or the common rail to decrease the fuel pressure when the fuel pressure in the fuel pipe and the common rail exceeds a predetermined limit pressure. Such an abnormally excess pressure may be caused by a malfunction on the inlet metering valve. For example, if the inlet metering valve is completely opened due to a mechanical malfunction or a short circuiting, the high-pressure supply pump feeds excessive amount of fuel into the common rail and raises the fuel pressure. The pressure limiter prevents excessive increase of the fuel pressure and assures the reliability of the common rail type fuel injection system.
That is, in a completely opened state of the inlet metering valve with the multi-cylinder engine rotating at an idle revolution speed, the pressure limiter enters an opened valve state because the pressure of fuel in the common rail exceeds the limit setting pressure, letting fuel flow from the fuel pipe and the common rail to the low-pressure side so that the pressure of fuel decreases to a level not higher than the limit setting pressure. As a result, it is possible to assure the reliability of the common rail type fuel injection apparatus.
With the conventional common rail type fuel injection apparatus, however, in an idle state with a small pump fed volume, the pressure limiter enters an opened valve state and a closed valve state alternately in a repeated manner. For example, due to a small pump fed volume, the common rail pressure may swing between an open pressure and a close pressure of the pressure limiter during the engine is operated under an idling state as shown in FIG. 7. Thus, the pressure of fuel in the common rail and the fuel injection volume become unstable, raising a problem of the engine""s rotational instability. At the same time, the increased number of times the pressure limiter enters an opened valve state and a closed valve state alternately causes spring fatigue and a bad seal seat, raising a problem of impossibility to assure reliability of the pressure limiter.
In addition, if the inlet metering valve provided at the inlet of the high-pressure supply pump is an electromagnetic valve of the normally closed type, a breakage of a wiring harness connecting a pump driving circuit to the inlet metering valve results in no fuel discharged from the high-pressure supply pump so that it is impossible to sustain a common rail type fuel pressure and a fuel injection volume, which are required to operate the multi-cylinder engine. As a result, there is raised a problem called an engine stall.
In the case of a normally open electromagnetic valve employed as the inlet metering valve, the high-pressure supply pump supplies fuel at an excessively high pressure or at a maximum flow rate in the event of an abnormality as shown in time charts of FIGS. 13 and 14. Examples of the abnormality are an abnormality of a completely open state of the inlet metering valve and an abnormality of a completely closed state of the inlet metering valve. The abnormality of a completely open state of the inlet metering valve is typically caused by a broken wire harness for supplying a pump drive signal from an electronic control unit (ECU) to the inlet metering valve or an abnormality of control executed by the ECU. On the other hand, the abnormality of a completely closed state of the inlet metering valve is typically caused by a foreign substance inadvertently between a valve body and a valve seat of the inlet metering valve.
In the conventional common rail fuel injection system, however, a fuel discharge caused by a valve opening operation of the pressure limiter and a fuel leakage caused by an abnormality and/or a failure of a high-pressure pipe route cannot be distinguished from each other. An example of the abnormality and/or the failure of a high-pressure pipe route is a burst of a high-pressure pipe. For example, a fuel discharge caused by an opened valve state of the pressure limiter may be detected as a fuel leakage by leakage detection logic as shown in the time charts of FIGS. 13 and 14, and a failsafe measure such as an operation to stop the engine is taken. However, there is raised a problem of the driver""s excessively aroused anxiety. When the pressure limiter is put in an opened valve state due to an excessive pressure applied by the high-pressure supply pump, for example, it is desirable to let the vehicle continue its running state so as to realize the limp home running of the vehicle.
It is thus an object of the present invention to provide a fuel injection system capable of assuring reliability of a pressure safety valve by eliminating idle performance instability caused by operations to open and close the pressure safety valve repeatedly.
It is another object of the present invention to provide a fuel injection system capable of avoiding an engine stall and putting the vehicle in a smooth limp home state in the event of an excessive pressure feed of the high-pressure supply pump.
It is still another object of the present invention to provide a fuel injection system capable of improving reliability and safety by execution of engine control whereby implementation of failsafe control is changed in accordance with the type of a fuel pressure decrease.
It is yet another object of the present invention to provide a fuel injection system capable of improving reliability and safety by identifying an abnormality which may be caused by an operation of a pressure safety valve or a state of an excessively high pressure feed supplied by a high-pressure supply pump from several abnormalities of the fuel injection system, and by providing an appropriate failsafe control.
In accordance with a first aspect of the present invention, when a high-pressure supply pump excessively supplies high-pressure fuel to an accumulator or when an abnormal pressure increase in the accumulator is detected, an idle revolution speed is raised to a value higher than a steady state speed. The fuel discharging performance of the high-pressure supply pump is increased due to the increased idle revolution speed. As a result, a pressure safety valve is maintained in opened state. By eliminating the accumulator""s fuel pressure instability caused by operations to open and close the pressure safety valve repeatedly as well as instability of the fuel injection volume and by eliminating instability of the idle performance, reliability deterioration of the pressure safety valve can be reduced. Therefore, the reliability of the accumulator fuel injection system can be improved. An operation to raise the idle revolution speed to a value higher than the steady state speed is equivalent to an operation to increase the fuel injection volume to a value greater than the fuel injection volume at the idle revolution speed in a steady state by at least a predetermined amount. In other words, an operation to raise the idle revolution speed to a value higher than the steady state speed is equivalent to an operation to increase the duration of an injector driving pulse or the width of the injector driving pulse to a value greater than a pulse duration or a pulse width corresponding to the idle revolution speed in a steady state by at least a predetermined duration or width.
The high-pressure supply pump may be provided with a metering valve for adjusting a fuel amount discharged from the high-pressure supply pump. The metering valve may be an inlet metering valve. The inlet metering valve is provided on an inlet side of the high-pressure supply pump. The inlet metering valve adjusts the injection volume of fuel introduced into the high-pressure supply pump so that the volume of fuel discharged from the high-pressure supply pump to the accumulator is adjusted. The metering valve may be a discharged fuel metering valve. The discharged fuel metering valve is provided on the discharge port of the high-pressure supply pump. The discharged fuel metering valve adjusts the volume of fuel discharged from the discharge port of the high-pressure supply pump to the accumulator. The metering valve may be a normally open type valve. The pressure safety valve may be configured to regulate fuel pressure in the common rail when the pressure safety valve itself continuously opens.
In accordance with another aspect of the present invention, an inlet metering valve or a discharged fuel metering valve is used to adjust fuel amount supplied to the accumulator. The inlet metering valve or the discharged fuel metering valve is implemented as a normally open type. The system has a pressure safety valve which has a pressure regulating function capable of sustaining the pressure of fuel in the accumulator at a regulated level in the event of a completely opened state abnormality of the inlet metering valve or the discharged fuel metering valve. Even if the pressure safety valve is once put in an opened state, the vehicle can be put in a limp home state.
The regulated level is a pressure required to put the vehicle in a limp home state in a state of an emergency requiring an urgent rescue such as an excessive pressure feed of high-pressure fuel supplied by the high-pressure supply pump to the accumulator. The regulated level is higher than an injector operating pressure but is such a sufficiently low pressure that a noise, a knocking sound and the like are not generated. The completely opened state abnormality of the inlet metering valve or the discharged fuel metering valve is an excessive pressure feed of high-pressure fuel supplied by the high-pressure supply pump to the accumulator or an abnormal pressure increase in the accumulator.
In accordance with a still another aspect of the present invention, a leakage quantity finding means computes a quantity of a fuel leakage from a high-pressure pipe route on the basis of an engine operating state detected by an engine operating state detection means, a high-pressure supply pump operating state detected by an operating state detection means or the high-pressure pipe route fuel pressure detected by a fuel pressure sensor. If a quantity of a fuel leakage computed by the leakage quantity finding means is greater than a first predetermined value but does not exceed a second predetermined value, a small fuel leakage from the high-pressure pipe route is determined to exist and a failsafe measure such as an action to limit the output of the engine is taken. If a quantity of a fuel leakage computed by the leakage quantity finding means is greater than the second predetermined value, a large fuel leakage from the high-pressure pipe route is determined to exist and a failsafe measure such as an action to stop the engine is taken. Thus, the engine can be controlled by executing the failsafe control in different ways in dependence on the quantity of a fuel leakage. In particular, when a small fuel leakage from the high-pressure pipe route is determined to exist, the engine is not stopped but the output of the engine is limited. Thus, it is possible to allow a running state to continue in order to realize limp home running. When a large fuel leakage from the high-pressure pipe route is determined to exist, the engine is stopped. This is because a large fuel leakage may be conceivably caused by an engine abnormality including an abnormality and/or a failure of the high-pressure pipe route. As described above, an example of an abnormality and/or a failure of the high-pressure pipe route is a burst of a high-pressure pipe. As a result, it is possible to improve the common rail fuel injection system reliability and safety.
In accordance with a yet another aspect of the present invention, a leakage quantity finding means computes a quantity of a fuel leakage from a high-pressure pipe route on the basis of parameters representing at least one of an engine operating state detected by an engine operating state detection means, a high-pressure supply pump operating state detected by an operating state detection means or the high-pressure pipe route fuel pressure detected by a fuel pressure sensor. If a quantity of a fuel leakage computed by the leakage quantity finding means is greater than a predetermined value and the high-pressure pipe route fuel pressure detected by the fuel pressure sensor exceeds a predetermined pressure level, a pressure decrease caused by an opened state of a pressure safety valve or an excessive pressure feed state by the high-pressure supply pump is determined to exist and a failsafe measure such as an action to limit the output of the engine is taken. Thus, if the pressure safety valve is opened in an excessive pressure feed supplied by the high-pressure supply pump, the fuel pressure in the high-pressure pipe route decreases due to an opened state of the pressure safety valve, that is, if a fuel escape exists due to an opened state of the pressure safety valve, the engine is not stopped but the output of the engine is limited. Thus, it is possible to let the vehicle continue its running state so as to realize the limp home running.
If a fuel leakage quantity computed by the leakage quantity finding means is greater than a predetermined value and the high-pressure pipe route fuel pressure detected by the fuel pressure sensor does not exceed a predetermined pressure level, a system abnormality including an abnormality and/or a failure of the high-pressure pipe route is determined to exist, and a failsafe measure such as an action to stop the engine is taken. As described above, an example of an abnormality and/or a failure of the high-pressure pipe route is a burst of a high-pressure pipe. As a result, it is possible to improve the common rail fuel injection system""s reliability and safety.
The predetermined pressure level may be a pressure value greater than an upper limit of a range used normally in the fuel injection system but smaller than the pressure safety valve opened state pressure corresponding to a limit setting pressure. Thus, the predetermined pressure level is never equal to a pressure value within the a range used normally in the fuel injection system and never becomes equal to or exceeds the pressure safety valve opened state pressure corresponding to a limit setting pressure. In addition, when the high-pressure pipe route fuel pressure detected by the fuel pressure sensor exceeds the predetermined pressure level, the fuel pressure in the high-pressure pipe route can always be determined to be abnormal. Thus, the control precision of the fuel injection system can be improved without regard to the detection precision of the fuel pressure sensor.
The predetermined pressure level may be set for each vehicle or each engine in accordance with the fuel pressure sensor output characteristic and the pressure safety valve opening characteristic, which vary from vehicle to vehicle or from engine to engine. Thus, since it is possible to set a predetermined pressure level for a vehicle or an engine by considering the particular output characteristic of the fuel pressure sensor of the vehicle or the engine and the particular opening characteristic of the pressure safety valve of the vehicle or the engine, the fuel pressure in the high-pressure pipe route can always be determined to be abnormal when the high-pressure pipe route fuel pressure detected by the fuel pressure sensor exceeds the predetermined pressure level.
An injection volume determination means may be constructed to find an injection volume of fuel injected to an engine from an injector of each cylinder on the basis of the engine operating state detected by an engine operating state detection means whereas a leak quantity determination means computes a quantity of a fuel leak from a high-pressure pipe route on the basis of the engine operating state detected by an engine operating state detection means, the injection volume calculated by the fuel volume determination means and the high-pressure pipe route fuel pressure detected by a fuel pressure sensor. Thus, the quantity of the fuel leak from the high-pressure pipe route can be computed with a high degree of precision.
A leakage quantity finding means may be constructed to compute a quantity of a fuel leakage from a high-pressure pipe route on the basis of an engine operating state detected by an engine operating state detection means, a fuel injection volume calculated by a fuel volume determination means, a fuel pressure fed volume calculated by a pressure fed volume determination means and a fuel leak quantity calculated by a leak quantity determination means. Thus, the quantity of the fuel leakage from the high-pressure pipe route can be computed with a high degree of precision.